Determining an amount of air entering an engine, and in particular an amount of air in cylinders of the engine, may be useful for various aspects of engine control. For example, the fuel control and fuel delivery may be coordinated based on a cylinder air charge to maintain a desired air to fuel ratio (AFR). Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted cylinder air charge and improving peak power outputs. The cylinder air charge depends on a boost manifold volume of the engine system. As the boost manifold volume increases, it takes more time for the boosted intake air held in the intake boost manifold to enter the cylinder. Conversely, as the boost manifold volume decreases, the boosted intake air may enter the cylinder faster. Thus, accurate estimation of the boost manifold volume may affect determination of the cylinder air charge, and thus fuel injection.
Other attempts to address estimating cylinder air charge in an engine include calculating the cylinder air charge based on a manifold filling model. One example approach is shown by Messih et al. in U.S. Pat. No. 5,331,936 A. Therein, the cylinder air charge is predicted based on parameters including previous cylinder air charge, manifold volume, engine speed, manifold pressure, and engine displacement.
However, the inventors herein have recognized potential issues with such methods. As one example, Messih et al. assumes that the manifold volume is constant. However, customer installed aftermarket boost manifold components may alter the boost manifold volume. Without a proper strategy to compensate for changes in the boost manifold volume, cylinder air charge may not be accurately estimated, which may lead to deteriorated engine performance. Still other situations may affect manifold volume.
In one example, the issues described above may be addressed by a method for an engine comprising: updating a boost manifold volume in response to a difference between an expected surge frequency and a measured surge frequency; and adjusting engine operating parameters responsive to the updated boost manifold volume. In this way, engine boost manifold volume may be updated while operating the engine.
As one example, during an engine surge event, the method calculates an expected surge frequency based on a known or currently estimated boost manifold volume. The method also monitors sensor outputs and determines an actual surge frequency. By comparing the expected surge frequency and the actual surge frequency, the method may determine if there is a change in boost manifold volume and may update the boost manifold volume if necessary. Based on the updated boost manifold volume, a more accurate cylinder air charge may be estimated. Engine operating parameters, such as a fuel injection amount as controlled via electronically actuated fuel injectors of the engine, may be calculated based on the estimated cylinder air charge. The technical effect of updating the boost manifold volume during a compressor surge event is that less offline calibration may be required in response to a change in the boost manifold volume and further that the system can automatically accommodate such changes and compensate for them in real-time. The technical effect of updating engine operating parameters responsive to the updated boost manifold volume is that that deterioration in engine performance due to a change in boost manifold volume may be reduced. Moreover, in some examples, the method requires no special equipment dedicated to estimating the boost manifold volume.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.